Tuesday, August 9, 2016

A New Wrinkle in the Megaraptor Mega-Mystery

credit Coria & Currie. Murusraptor CC 4.0

Definitely shaping up to be the year of clan megaraptoridae with new species and information seeming to come down the pike on a weekly basis. When such a glut of data comes at us at such in such a breakneck pace and when - in the case of megaraptorans - such large questions remains such as "what the hell are they actually?" it does pay to sometimes take a breather and digest things a bit. By slowing down and picking things over details that might otherwise be glossed over might see the light of day. It is one such detail that I want to highlight in this post. It does take me into territory that I certainly don't specialize in nor have the inclination or background to really get into - cladistics.

Yup, in life you gotta know your strengths and weaknesses and, no disrespect to the hard work others put into this aspect of paleontology, it's simply not my bag folks. So no, don't expect any data matrix from me folks or some prolonged digression into some obscure processes or foramen. I like the "softer" aspects such as functional stuff, appearance, behavior, and ecology. That being said the one feature I want to highlight in this short post is a feature that bridges the adaptational approach which influences my thinking and the - no disrespect to practitioners - the bean counting of cladistics with its emphasis on character traits, data matrices, parsimony analysis... yawn I can almost feel myself getting sleepy just talking about it.

Megaraptorans have some pretty neat teeth to talk about, not so much for the features that they have, but for the features that they lack.

Megaraptoran teeth lack interdenticular sulci (White et al., 2015).

On lateral teeth:

"There are no interdenticular sulci between any of the denticles on the distal carina"

From the discussion:



As I keep saying (and feel free to say it along with me) : It really is all about the teeth.



Readers who have been following me for a while will no doubt recognize the importance of this dental feature in tracing my evolving line of thinking on the range of functional ability and carcass utilization in theropods that featured such adaptations. My first real exposure to this dental adaptation in theropods by a paper by Brink et al. (2015) Developmental and evolutionary novelty in the serrated teeth of theropods which I discussed in my post Death Comes Ripping: Bonesaw Theropods. Basically interdenticular sulci are recesses between the denticles that arise developmentally. They serve to alleviate stress and overall strengthen and prolong the life of the denticle and therefore cutting proficiency of the tooth over its lifespan and we see rough analogy in expansion slots built into bone saws and cutting blades. Such features are not found in sharks, monitors, and sabertooth cats therefore creating the argument that serrated theropod teeth are on a functional level superior to the the teeth of these animals in cutting longevity. Which makes perfect sense because it is theropods that had to carve up and butcher the largest, thickest skinned, bone plate armored, cartilaginous and tendinous food base the world has ever seen - their herbivorous brethren. Bone is just another tissue in this regard just as likely to be sawed through as armor plated skin or thick tendons and joints as enamel trumps all these tissues in hardness scale. It's not a mistake that a great many theropods had a head narrow side to side but thick and strong from top to bottom that bears some uncanny resemblance to a blade or hatchet. Bonesaw theropods are not likely right because they are "awesome-bro" but because from an adaptationist approach animals with such tough rinds were what they had to cut through on a day to day basis and we should expect their enamel covered (and therefore likely lip covered) teeth to do the task that was set out before them.

credit Brink et al. 2015 interdenticular sulci in theropods


An inference I am going to make is that megraptorans - as the most common large carnivore in their ecosystem in many places (but especially Australia) likely fed on titanosaurs (alive or dead it don't matter). Titanosaurs certainly had a tough rind and lots of evidence of osteoderms in that family.

From discussion White et al., 2015:


The logical question arises that if megaraptorans evolved from some putative tyrannosauroid or carcharodontosaurid why would they lose their interdenticular sulci with such a food base? The answer of course is that they would not lose such a feature that benefitted hypercarnivory and that they did not evolve from a hypercarnicorous carcharodontosaurid or tyrannosauroid. That still leaves open the potential of evolving from a tyrannosauroid that did not have interdenticular sulci and which was a small game scrounger - a possibilty White et al. allude to:


While evolving from a basal tyrannosauroid that lacked interdenticular sulci is still possible it might be more promising to look at even more basal common ancestors as a distinct possibility - a putative small game hunting coelurosaur. Something like Compsagnathus, Juravenator, or Scipionyx? Brink et al. (2015) suggested interdenticular sulci as a synapomorphy of theropods secondarily lost by troodontids and spinosaurids. However in their study they did not investigate basal coelurosaurs which might lack sulci due to their small prey diet. I don't know for certain if some coelurosaurs lack sulci? Anybody have any info on this question out there?

If some coelurosaurs lacked sulci a putative basal small prey coeulurosaur might just be the subject we are looking for. Such a culprit might produce the blending of features that have caused various analyses to suggest spinosaurid, carcharodontosaurid, and tyrannosauroid affinities. Such a culprit might make a good island hopper/rafter and colonizer (e.g. Japan/Australia) as several compsagnathid species do seem to have excelled at colonizing islands. Evolving from a small game hunter that lacked interdenticular sulci is consistent with the strange anomalous lack of interdenticular sulci in megraptorids given a likely "brontophagist" niche. Given enough time megaraptorids may have independently evolved interdenticual sulci but as they were possibly just recently patriated to brontophagy from (potentially) a small game hunting ancestor they only had simple serrations.

And if megaraptorids did indeed arise from a generalized, island hopping, small prey eating putative coelurosaur this sort of makes megaraptorids their own thang right? Not some obscure offshoot of carcharodontosaurids or tyrannosauroids but their own rightful clan of unique hypercarnivorous theropods. Not claiming this idea as unique to myself as I think several other bloggers/researchers have put forth the same idea of megaptorids being their own thing. But I think looking at the tooth adaptation adds another layer of evidence in favor of megaraptors being their own clan.

A final caveat is that just because megraptorids lacked interdenticula sulci does not suggest that they were inferior carcass renderers than theropods that had them. It merely means that their denticles did not last as long and something as simple as higher tooth replacement rates could have kept them equipped for efficient brontophagist shenanigans.

a very "coelurosaur looking" Megaraptor credit Tom Parker, 2015 CC 4.0


papers

Coria RA, Currie PJ (2016) A New Megaraptoran Dinosaur (Dinosauria, Theropoda, Megaraptoridae) from the Late Cretaceous of Patagonia. PLoS ONE 11(7): e0157973. doi:10.1371/journal.pone.0157973

Brink, K.S.  et. al. (2015)  Developmental and evolutionary novelty in the serrated teeth of theropod dinosaurs.
Scientific Reports 5, article no. 12338, July 2015


White, MA, Bell, PR, Cook, AG, Poropat, SF, Elliot, DA, (2015) The dentary of Australovenator wintonensis (Theropoda, Megaraptoridae); implications for megaraptorid dentition PeerJ Dec 2015 online


"A Long habit of not thinking a thing wrong, gives it a superficial appearance of being right, and raises at first a formidable outcry in defense of custom". Thomas Paine

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Tuesday, August 2, 2016

Making Dromaeosaurids Nasty Again Part IV: New Hypotheses on Dromaeosaurid Feeding Technique & Role of Tail in Movement

Hey now... I really thought about splitting this post into two posts for both respective hypotheses, but for the sake of brevity and wrapping this series up I decided to combine them. Additionally, as I will elaborate on further, the two aspects I will focus in on here - biting & locomotion - are not mutually exclusive and one dovetails into the other. So I gave this article a really long title and hope you get something out of it!!

Readers of this series may have detected a slight yet pervasive diminution of the import of the famed "killing claw" over the course of these posts. In my first post I documented the shift in scientific thought on these claws from scythes that cut meter long slashes in prey to crampons that allowed hitching rides on the hides of dinosaurs to ultimately the prevalent modern interpretation of raptor prey restraint (RPR) model of Fowler et al. in which prey subequal in size is grasped by all four digits. I reiterated a point seldom mentioned from the Fowler et al. paper on the dromaeosaurid RPR hypothesis: relative to accipterids, the ungual grasping ability of dromaeosaurids was >not as strong< as these birds in that arena i.e. they were not simply scaled up hawks. Later in that post I suggested a role for the arm/wings for pummeling prey/combatants as the feet grasped and pinned the animal. In my next post focusing on aggressive/combative scavenging in these animals I focused in on digit II as a useful tool in pinning large carcasses down as the head, neck and teeth pulled back on flesh - an idea supported by the unique morphology of the denticles on these theropods and the presence of enlarged digit II claws in several birds that work in a similar fashion.

My contention is that the import of digit II - so highly regarded that it is referred to as the "killing claw" - has both culturally and scientifically influenced these animals to the point that other aspects have been enshrouded. But was the "killing claw" really the most pivotal aspect of these animals behavior and ecology? I think not, or at least >not always<.

If the use of the "killing claw" digit II was indeed the be all and end all of dromaeosaurid prey capture and feeding technique we should be able to make some predictions to test that assertion. That over the course of the 100 million year evolutionary trajectory of these animals an increasing reliance on ungual prey capture will 1) show a trend towards shorter and therefore stronger legs i.e. less cursorial adaptations 2) as firepower is concentrated in the feet for killing the robustness of the skull and teeth should hold steady or potentially diminish.  In the early Cretaceous Deinonychus we have a relatively sub-cursorial but highly adept foot grasper - again there is a bit of an inverse relationship between foot grasping strength and cursorial ability as I discussed in the first post and which Fowler et al. highlighted in their paper. I will cut and paste the source of this observation from the Fowler et al. paper:


As evidence for the purported trend in increasing foot strength Fowler et al. cite Deinonychus (early Cretaceous), and Velociraptor & Saurornitholestes (late Cretaceous). While Deinonychus and Velciraptor have relatively short metatarsi I can't see how they interpret the leggy Saurornitholestes as an example of this trend. Additionally there are some notable omissions, most obviously the name sake for the whole family Dromaeosaurus!!

In Dromaeosaurus albertensis cursorial adaptations are highlighted, the killing claw is relatively atrophied, and the skull is relatively massive and robust (almost tyrannosaurid like as GSP has commented). I mean just check out the skull of this animal, there is nothing slight, superficial, or atrophied about it at all:

robust head of Dromaeosaurus albertensis. credit LadyofHats. public domain
relatively diminished claw size/strength D. albertensis. credit LadyofHats. public domain
On the other hand digit II is not especially robust in Dromaeosaurus and the remaining unguals look more adapted towards a cursorial lifestyle than grasping. A "ground hawk" this was not.

Several of these trends towards diminished ungual strength and/or increasing skull robustness also play out in Dakotaraptor (cursorial w/diminished foot grasping ability) and the very robust skulled Atrociraptor.

Atrociraptor credit Ferahgo the assassin (Emily Willoughby) CC3.0
What am I getting at here? If anything the trend is towards increasing tooth and skull reliance over time >not always< towards increasing foot grasping & "killing claw" importance. I say >not always< because there were and likely always were dromaeosaurids that highlighted foot grasping ability. Sometimes foot grasping became diminished, sometimes it was very important. But what was always important and what was always highlighted in these animals was the jaws and teeth. They are the feature that always stayed pat or, if anything, increased in prominence.

No dromaeosaurids were not evolving protobeaks or going edentulous despite the persistent artistic meme and no they were not diminishing emphasis on teeth and jaws.

It really is all about the teeth....

To drive home this contention I want to revisit a famed piece of data that has caused quite a stir in terms of whom and how it was done - the famed Tenontosaurus bite marks and the case for Deinonychus "bite strength". A technical paper by Gignac et al. (2010), a blog post by Mark Witton, a blog post by central coast paleontologist, and an internet article/summary from The World of Animals all highlight the attention and thought these remains have attracted.

That these bite marks have evolved into a bit of a paleontological "who done it" has always irked me. Not because of a lack of data or some systemic problem with the analysis - but because of the pervasive "explaining away" of data that most parsimoniously points to Deinonychus as the perpetrator. Several  ideas have been bandied about in an attempt to account for these bite marks by Deinonychus, a predator that appears to not have an especially high bite force.

Let's unpack them:

1) An undescribed and undiscovered tyrannosauroid dinosaur did this damage.

We have seen this story before... tremendous damage to bone - no way a "blade toothed" theropod did it much less a puny dromie. Let's just imagine a stout toothed, bone crunching tyrannosauroid existed at a time when such animals were basically all blade toothed anyways, and make this essentially fictional animal the perpetrator. Made up tyrant lizards did it!! Pesky blade toothed theropods just stay in your lane - you guys can't bite through bone the way tyrant lizards can!!

As you can tell (snark alert) I am not so much a fan of this idea. We have evidence of Deinonychus being the most ubiquitous theropod in the area; the tooth arcade matches; broken teeth in the area; the well established Tentontosaurus - Deinonychus relationship - the whole tide of evidence points to Deinonychus. If a cryptic lineage of stout toothed, bony crunching tyrannosauroids existed at this time I will be happy to be proven wrong - as of now I know such evidence and of the tyrannosauroids from this time period they are blade toothed predators without expanded jaw musculature - although I have heard murmuring of tyrannosauroid teeth from the same formation (but blade toothed not lethal bananas).

2) Deinonychus could bite hard, but it did so extremely rarely.

I mean really? Remember when you kept hearing how humans only use 10% of their brain? Yeah, this explanation sounds a lot like that. Over designed with a bite force exceeding modern American alligators yet barely ever uses this strength? I can't really go with this thought.

3) Stronger bite than predicted from studies.

I don't think that this animal had much of a stronger bite than studies indicate. I believe that we have been a little bit more than led astray by always looking at static bite strength as opposed to other methods of cutting that highlight speed, friction, and getting those darn denticles to do the work for you. It really is all about the teeth and it really is all about getting the denticles to work in a way that maximizes cutting efficiency with minimal effort and wear & tear of the tooth.

Its high time we start looking at hypotheses that invoke Deinonychus as the prime perpetrator. I will  put out a hypothesis that highlights an unorthodox feeding mechanism in these animals, that is consistent with the data, and offers much explanatory power for the observed data.

To prime you for it I want to look at birds a bit (as usual). To really confound the situation the obvious choice is flamingoes - because what better to compare dromaeosaurids to than flamingoes, amirite?!?



I mean, excuse the poor video quality, but just look at those tongues go!! It is the tongue just pumping back and forth causing the whole neck to just vibrate. I have no idea why these flamingoes engage in this lingual vibration? Anyone ever see wild flamingoes do this? I would have to assume that they pump their tongues back and forth to filter food but in my observations of these captive Chilean flamingoes they just do it while walking around... probably just bored.

No I am not suggesting that Deinonychus had some sort of lingual vibrational apparatus set up - just pointing out how one muscular organ - the tongue - can move with such speed and power in this bird that it vibrates the whole head and neck of these animals. I mean can your tongue move with such speed and power that it causes the whole body to hummm and vibrate... ummm never mind. The message I am trying to convey here is that when we look at avian feeding mechanics - and by extension many dinosaurs and especially paravaians/maniraptorans/dromaeosaurids - there is a lot of potential for quick twitch muscle, full body and/or neck movement involved in the feding apparatus.  To drive home this point, literally, what would woodpeckers be without their exceptionally quick and rapid - fire neck movements? Yes, it is the skull of woodpeckers that is wonderfully equipped to handle the blows and stresses incurred but without the power and speed provided by the neck the woodpecker would, essentially, not peck. It would just be a bird with a strong skull.


An often overlooked aspect of feeding mechanics is elaborating on how parts of or the whole of the body is engaged in feeding mechanics - the head need not be looked at as an isolated aspect of the process. Regular readers should note that I have made this point before on antediluvian salad especially with regards to twist or torsional feeding (death rolls) in plesiosaurs and in my bonesaw shimmy hypothesis on Allosaurus in which it is rapid neck movement in both the fore and aft direction that allows the denticles on the front and back end of the tooth to saw right through tissue. Bite force was not especially important in that hypothesis, in fact tight clamping would work against free movement of the denticles over the tissue.

This hypothesis does take some inspiration from the bonesaw shimmy model but it does deviate from it in several ways.

I propose that fast twitch muscular contractions of the neck, torso, and even tail would pulse out vibrational waves of energy towards the head. As bipeds that do not have their front feet on the ground these pulses of vibrational energy would travel unhindered through the neck, head, teeth, and ultimately into the food item they are cutting into. As the vibrational energy literally vibrated the tooth back and forth into the food item the peculiar denticle pattern of dromaeosaurids comes into fruition as an optimized adaptation to literally bore and auger into tissue.


The most striking and unique feature about the denticles on Deinonychus is that they are fairly reduced on the front of the tooth but very pronounced on the rear. But even stranger is the manner in which they are curved on the rear side which is towards the tip of the tooth, referred to as apical hooking. Fowler et al. suggested that this unique denticle design would optimize cutting into tissue as the prey animal was held in the RPR model and the head of the dromaeosaurs was sub-vertical with the nose facing down and biting between the legs. However this suggestion by Fowler fails to address the issue that many other theropods likely held prey/food down with their feet and wrenched off bites in a sub-vertical manner yet these theropods did not evolve such weird denticles as seen in many dromaeosaurids.

But if we imagine each denticle as a "tooth" and each tooth having a respective duty in food processing a potentially new perspective emerges that could explain the unique bone damage ascribed to Deinonychus.


As the piece of food is grasped a strong bite is first established. The slight and reduced serrations on the front of the tooth are useful here in establishing a piercing bite - not very deep as their bite force was modest but merely a small indentation into the article of food. Once a purchase is made then the body commences vibrations - potentially a combination of head, neck, torso, and tail rapid fire twitches - which allow the tooth to bore and auger into the food particle i.e. bone. As the "bore hole" phase commences the utility of the weird apically hooked denticles comes into play as each denticle literally chips and shreds away at tissue like individual teeth. As the tooth works its way into the material it leaves a remarkably accurate impression of the tooth - a literal bore hole that for all intents and purpose can be read as a puncture. Once the integrity of the material is weakened substantially the item can be pinned with the arms and/or feet and the head and neck are pulled back strongly incurring further and more drastic damage as the tooth is dragged back through the (weakened) material literally leaving deep bone raking marks and furrows. It is also potentially possible that vibrations of the body were not emphasized or were in fact used in concert with multiple quick bites - essentially chattering of the jaw - in which micro - abrasions from the denticles work to carve into tissue.

This "vibrational feeding" hypothesis could potentially explain the two types of feeding traces recorded on the bones of Tentontosaurus which include longer gouges and simple punctures.



Above you see the type of "bone rakings" I mentioned earlier. An initial puncture is established and with the teeth embedded now the neck and body can pull back and rake through tissue.

What I suggest was occurring here is that these were investigative bites into bone. The theropods were gouging into the bones to see if there was ample nutritional value in them to justify the effort and potential wear of teeth. There would always be a three-way tradeoff between nutritional value versus the effort and wear on the animals feeding apparatus all of which is tempered by the relative health of the animal i.e. how desperate for food is it. Ultimately it looks like the theropods abandoned the bone consumption in this case.





That dromaeosaurid teeth occasionally show extreme wear - especially on the tips as should be predicted in this model - is very interesting.

worn tooth "Dromaoesauroides" wiki
Private "dromaeosaur" tooth Montana .84"
Judith River "dromaeosaur" tooth 
Clearly these animals were putting some heavy wear on their chompers, especially when we account for the fact that they were not keeping their teeth for life. An interesting test would be to see if komodo dragon teeth ever show equal levels of wear. But again, not the best test because theropod teeth were actually superbly designed to withstand stress more than any other ziphodont predators (Brink, 2015) (including komodos), yet they were still showing drastic wear... these animals were not getting this type of wear from just eating small animals and delicately nipping carcasses I'll tell you that much.

Of course it is worth mentioning that there is a lot of room for deviation in this model and we need not assume that all dromies employed vibrational feeding to the same extent. Indeed Dromaeosaurus could have employed a lot more emphasis on traditional "power chomps" than what I suggested for Deinonychus.

In theropods, being both ziphodont toothed and bipedal, there is no go to analogy among modern tetrapods - birds don't quite tell the whole story and neither do monitor lizards. So maybe we should expect some unothodox feeding mechanics.

Lifestyles of not only the quick and cursorial but the slow and persistent as well...

And now for the tail. Probably the aspect >least likely< to be assumed to be involved in "making dromaeosaurids nasty again". But it is the tail that is the most important aspect of these animals I will argue. The tail is what really pulls together all the disparate attributes of these animals and makes them what they were. And what they were was quite literally the most successful in tenure small to medium sized terrestrial hunter - scavengers that have ever existed. A unique blend; of accipterid "raptor"; combative scavenging vulture; bone chomping hyena ; a dash of felid; and, yes, highly efficient cursors similar to kangaroos, hyenas, humans, wolverines, and Arctodus.

One of the persistent ideas that has gained popular recognition in recent years is that dromaeosaurids were sub-cursorial - that they were slow. A chief argument put forth to support this notion is that the ankle bones - the metarsii - were rather short. And this is true for many species - Deinonychus and Velociraptor in particular - that were gaining mechanical advantage of foot claw strength at the expense of speed. But this was not so true in several other species - Dakotaraptor and Dromaeosaurus for instance - that were leggy to an exceptional degree. I am just not at ease with suggestions that species at the lower end of the spectrum were heavy footed clunkers - they could probably all put on a decent burst of speed if need be. Ursids (da' bears) have all the hallmarks of real clunkers but put on good speed with their short ankles. Keep in mind that dromies were competing with larger - and in the case of tyrannosaurids likely larger and quicker - theropods as well as azhdarchids. It is not always about being the fastest - but about being more agile when fleeing a larger threat. With their arm - wings and long tails doubtless many dromies frustrated an angry tyrannosaurid back in the day with their superior agility.

The dromie tail, just like the dromie "killing claw" has gone through a twisted and convoluted history of interpretations and revisions. A brief recap. Ostrom interpreted the tail as an intricate balancing rod that facilitated use of the "killing claw" for kicking and hanging onto prey. Each subsequent interpretation of dromie killing technique from hanging onto the side of prey and biting to the RPR method invoked the tail as intricate balancing organ for their respective prime foraging technique.

To add further context to the strange saga of dromie tails I want to revisit a post from Pterosaur.net Blog  (remember that great site?) Dragon Tails: What Pterosaurs Teach Us About Velociraptor that made the strange and startling comparison between dromaeosaurid tails and rhamphorynchid tails... wtf? Well there is a comparison to be made there and it is not soooo strange when we work from the starting point that dromaeosaurids likely had flighted ancestors... so that they inherited a tail that - presumably - shared a convergence in form and function with rhamphorynchid pterosaurs.

credit Scott Hartman used w/permission . blog Scott Hartman's Skeletal Drawing

credit Scott Hartman used w/permission . blog Scott Hartman's Skeletal Drawing


So if dromaeosaurids inherited the weird morphology of their tails from flighted ancestors - full of chevrons, diminished musculature, partially ossified dual tendons (i.e. caudal rods) there becomes two rather interesting questions: 1) what adaptive benefit did these features incur in flighted dromaeosaurids and tailed pterosaurs? and 2) how was this morphology coopted into terrestrial based dromaeosaurids? Question number #1 I am going to leave alone but I think it is a long overdue question that needs analysis but question number #2 is what I am going to approach here.

credit Scott Persons

What I am going to suggest is that dromaeosaurids across all ranges of absolute speed and leg length - were highly efficient long distance pacers. They could and did just keep going for miles at a time at a relatively moderate pace. The whole lot of 'em could just run you to death. And the key to this long distance efficiency was the tail. The tail - the whole organ - served as an elastic recoil that allowed these animals to store, redistribute, and recoup energy for efficient, long distance traveling. I have seen scant attention to the tail as an aide in terrestrial efficiency in dromies. Despite the fact that these animals were terrestrial and the tail of dinosaurs is intimately linked with movement - especially per the caudemofemoralis muscle. Darren Naish raised the question of dromie tails back in 2008 (What the hell is going on with dromaeosaur tails?) in light of Norell & Makovicky (1999) describing an articulated and sinuous Velociraptor tail. The comment section is interesting. I do note in it a pervasive sentiment of trying to "explain away" the sinuous tail - the presupposition being that stiff tails is the better supported null in dromies to start with. But is a stiff tail the better supported null or is it just how we grew up expecting dromie tails to behave? In either case lateral flexibility shown in both Velociraptor and Bambiraptor seems to have prevailed. But there is one comment by Alan #19 that I believe was very prescient and which received literally no attention in the discussion.




I think Alan was on the right track as goes energy efficiency although I doubt the hopping dromie scenario has much merit - indeed trackways have proven otherwise.

I will be working from the assumption that dromaeosaurids - whatever abilities they had for arboreal behavior or even some amount of gliding or even "flight" in small ones - that they were basically terrestrial animals and that the tide of evolutionary impetus should create a better and more efficient terrestrially adapted animal. Not an evolutionary experiment, and not a maladapted kinda-climber, kinda-jumper, kinda-walker but a reasonably well equipped and efficient animal that could do all the things that we should expect a small to medium sized hunter - scavenger to do in a highly competitive ecosystem. In short they could climb, they could potentially even swoop, they could swim, but what they did the most was walk and run around. Namely that means that they could move fairly quickly and efficiently to highly localized food sources -   carcasses, hatching dinosaurs, large concentrations of prey. Especially given their long tenure, efficient terrestrial movement should almost be expected. Contra the "ground hawk" image we need not assume that these animals were >always< sit and wait ambushers or would swoop down from a perch. Indeed sit and wait ambushing is more of an ectothermic strategy and even when warm blooded predators do ambush from trees or from cover they choose spots that have a high degree of certainty that prey will be there fairly regularly. Dromies possibly could have utilized this tactic to some degree but I hardly think it was their dominant foraging strategy given that several species developed obvious cursorial adaptations and that some species lived in areas with little tree cover or sparse vegetation in general (i.e. dune fields).

From my own experimental paleontology in which I strapped on a huge tail to my butt at SVP Los Angeles and commenced to simultaneously entertain and annoy attendees I noted several patterns. What was really interesting to me is how much that darned tail moved around. Literally the smallest movement I made would thoroughly send the tail in motion. And what was most notable was the dramatic up and down oscillations that the tail went through as I walked. Each foot fall would create a simultaneous rise and fall of the tail - even the smallest and daintiest step. Don't believe me strap one on yourself and be a dinosaur for a day - you'll see what I am talking about.



These up and down movements of the tail that occurred simultaneously with each footfall likely occurred in all dinosaurs to some degree.  What is interesting is that dromaeosaurid tails - because of their "caudal rods" - were designed to diminish this up and down movement of the tail as thoroughly explained by Scott Persons on his post on dromie/rhamphorynchus tail convergence. Note in the pic below how the caudal rods are neatly stacked against one another on the vertical plane to limit movement dorso - ventrally.

Caudal rods in Deinonychus prevent up and down movement of tail
credit Scott Persons
As has recently been illuminated by discoveries of articulated tails of Velociraptor and Bambiraptor these tails could still bend quite sinuously in the lateral realm.

Bambiraptor tail credit Scott Persons
So if the caudal rods of Deinonychus and other dromies diminish the up and down movement of the tails - which is a natural consequence of bipedal movement - we have some missing kinetic energy to account for. Energy is neither created nor destroyed. Something has happened to the energy otherwise absorbed and dissipated by the tail through up and down movement with each footfall in dromaeosaurids... where does it go? I suspect that this energy is recouped into the legs and aides in giving these animals just a little extra "bounce" to their step. The tail may work as a wonderful elastic rebound organ. We should potentially imagine dromies being very bouncy and springy as they paced along.

This model of locomotory efficiency is not without parallel in animals that have to move across vast expanses to find and locate rare and ephemeral food resources. A leading hypothesis concerning Arctodus is that it was a highly efficient long distance pacer that scavenged and usurped carcasses (Matheus, 2003) utilizing long legs and elastic recoil to travel at a moderate pace over long distances. Hyenas have long been noted for their efficient loping pace that allows large scale movements and carcass retrieval. Kangaroos and wallabies are well noted for their ability to travel long distance at an extremely energy efficient pace owing a lot to the elastic recoil in their leg tendons. Indeed a robotic kangaroo has been designed that utilizes such elastic recoil in the tail to recoup energy for movement.


I would be remiss not to mention the endurance running hypothesis has been invoked as a strategy for both scavenging and pursuit hunting in our own genus aided by the achilles tendon. To further quell the notion that short legs - such as in Deinonychus or Velociraptor - imply a suboptimal terrestrial movement capability let us not forget about wolverines which are notorious long range hunter -scavengers despite being very short limbed. I don't know if there have been any studies on the locomotory efficiency of these animals but I suspect there is something to 'em in those regards. There are at least loads of references to the marathon travels of these facultative scavengers.



"It is absolutely impossible for any human to keep up with a wolverine. What wolverine can do is just beyond human."

"A wolverine crosses a topo maps like we cross a street."

"They devour the landscape at a constant 4 mph regardless of terrain."

An energetic bundle of tooth, claw, and attitude? Switching from small game foraging to large carcass acquisition as the seasons dictate? Bone consumption? Able to outpace, outcompete, and outwork competitors that are several orders of magnitude larger in size? Thriving in areas and desolate habitats that other predators eschew (snowfields analogous to dune fields in these regards)? A little bit of the Gulo gulo in your dromie? You bet.

Making dromaeosaurids nasty again... Invoking the wolverine as a likely analogue for many dromies, it doesn't get much nastier than the demon of the north.

Ichnology: What Does It Tell Us?

Xing et. al. (2013) document a variety of dromaeosaurid trackways from the lower Cretaceouls Hekou group in China. The pace was not very high at about .75 meters/second which is about 1.7 mph or 2.7 km/hour. Average human walking speed is said to be about 3.1 mph or 5.0 km/hour. Let me just cut and paste the discussion:

So although these particular dromies seem to be moving along at slowish pace - perhaps they had full bellies or were just walking down for a drink. It is noteworthy that they mention several dromie ichno-species in the last paragraph that seem to be cruising along at quite brisk paces and one zipping along pretty good.

Dromaeosauripus from Korea at 4.86 m/s (Kim et al. 2008) which is 10.9 mph / 17.5 kmh

Paravipus  (Murdoch et al. 2010) at 1.67 m/s and 3.61 m/s which is 3.6 mph / 5.8 kmh and 8.1 mph / 13.0 kmh

Dromaeopodus at 1.63 m/s (Li et al. 2007; Kim et al. 2008) which is 3.6 mph / 5.8 kmh

Considering that to document an actual predatory chase in the footprint record is exceptionally rare and that there is no evidence that a chase was in progress in any of these instances the ichnological data is very interesting. We see a range of speeds here from the more leisurely .75 m/s to a quite hectic 4.86 m/s. If we assume that these are reasonable cruising speeds then the small sample size we have does point to a relatively fast paced "cruiser" similar to humans, wolverines, coyotes, and hyenas that can cover vaste expanses of land at an efficient pace as the penultimate terrestrial hunter - scavengers of their time.

The Seldom Mentioned Fact of Dromie Toe & Heel Pads

The trackways from this study demonstrate that dromies had big ol' foot pads like two toed ostriches but also large heel pads! So pay attention to this aspect paleo-artists  >at least some< dromies had big fat derpy looking foot/heel pads that are universally never depicted at all or large enough in paleo-art depictions (including my own). Why has this well documented aspect of dromaeosaur foot anatomy never penetrated into popular depictions? I mean no one - literally nobody - including world renowned paleoartists or more obscure/enthusiast artists depicts dromies with large heel pads. Yup the toes had big padding but the heel pad would have been very apparent in life. And this is from a peer reviewed paper with several notable authors including most notably to my western biased eyeballs, Phil Currie (who is btw the last author).





Such fleshy and large toe/heel pads would assist in stalking behavior by muffling sounds, stability, absorb stress from cursorial activity but I also have to wonder if such fleshy structures would diminish grasping effectiveness?



Also check out the base of digit II often reveals a bit of a fleshy toe pad. Dromaeosauripus yongjingensis represents a fairly large "Utahraptor" size dromie but other dromie footprints reveal fleshy toe pads and heel pads.




Kim et al. did a paper with reference to a speedy little dromie in the above discussion (Kim et al. 2008) from Korea of Dromaeosauripus moving along at about 4.86 meters per second (10.9 mph or 17.5 kmph).

Abstract:

The question is though does this represent a cruising speed or were we in fact lucky enough to document one of the rare instances that a theropod was actually "on the hunt"? Or neither? Could it be that dromies would normally walk at a fairly leisurely pace of less than 2 mph but when spurred into action (i.e. carcass or prey that have been detected via sensory cues but still require covering large terrain) that they then shift gears into a relatively higher pace 3 - 4 mph or even up to 8 - 10 mph / 16 -18 kmph? That is pretty fast but I hardly think it represent the top speed of these animals.

I also should give some space to the ichnological data pointing to at least six large dromies traveling in parallel and the special emphasis the authors give to the toe and heel pads in the footprints ( Li, 2007).






So when depicting the average large terrestrial dromie foot think more about ostrich feet than harpy eagle feet. Except that unlike ostriches dromies often had big ol' heel pads in addition to toe pads that would have further cushioned the foot and added a degree of stability normally not ascribed to these animals. The increased surface area would have facilitated greater efficacy and stability of movement in dubious terrain such as dune fields and mud flats.

ostrich foot credit Masteraah CC 2.0
Again it does beg the question that - at least among the dromies that sported such large heel & toe pads - how efficient a grip could have been enacted with the claws in the RPR model? I mean having such big, cushy organs between your claws and the animal you are gripping does pose some practical questions as goes the efficiency of such a grip.

A lot of questions to be answered but I do think that a fresh appraisal of these animals as primarily terrestrial long distance hunter - scavengers that have to cover a lot of ground efficiently is needed. Optimal walking versus optimal cruising speed can be addressed with larger sample size of ichnological data and computational methods... What I can say is that the anatomy of the tail likely has something to do with terrestrial locomotion and efficiency of gait is as good of a hypothesis to investigate as any...

These animals had to have been able to move and move well. They had to have traversed wide distances to secure meals in often times inhospitable terrain. They had to have competed against larger and aggressively hungry and growing youngsters of  tyrannosauroids, carcharodontosaurids, and other theropods. They had to get to carcasses before large pterosaurs got all the good stuff. They had to have been at least reasonably competent in these realms to have persisted as... I don't know... the longest tenured group of small - medium sized tetrapod terrestrial hunter - scavengers that ever existed ( I know I said it before but it bears repeating). Speedy thieves indeed.

Earlier in this article I suggested that there was a link between the tail and biting apparatus in these animals - that their functions dovetail together. At the risk of piling one hypothesis on top of another let me put it out there that the diminished dorso-ventral movement of the tail as dictated by the caudal rods would have shunted more of the potential energy towards the anterior of the body - essentially towards the head, jaws, and teeth - during vibrational feeding.

credit Duane Nash Tsaagan & Velociraptor

Final Thoughts

Both a scientific and cultural emphasis on the "killing claw" in dromaesaurids has obscured a more nuanced, multifaceted, and holistic approach to these animals; that the "ground hawk" model has so embedded itself into our conscious; that the potential role of arm-wings as brutal spiked clobbering devices analogous to wing pummeling in modern aves has been overlooked; that the teeth were highly specialized and brutal weapons in their own right capable of extreme insults to carcass integrity (including bones) and perhaps full body "vibrational feeding"; that the importance of head and tooth weaponry did not diminish over the evolutionary history of this group but sometimes increased while emphasis on "killing claw" and foot grasping capability did in fact sometimes diminish; that cursorial ability did often times increase in capability and that all dromaeosaurids may have benefited from elastic rebound provided by caudal rods in the tail enhancing long distance, mid-paced terrestrial efficiency of movement as well as large fleshy toe & heel pads; that life appearance may have been more varied than simply "grounded hawks" with "dapper" haircuts but imbued with much of the panoply of life appearance we see in ratites, predatory and scavenging accipterids, cathartidae, bucerotidae, galliformes, and other large/terrestrial aves including but not limited to large exposed fleshy areas including caruncles, wattles, frills, dewlaps, and other tough - elastic - and fleshy skin derived outgrowths for thermorgulation and sexo-social signaling; that these attributes when generously applied to an outstanding and long lasted dynasty - in fact the longest tenure of small to medium sized tetrapod terrestrial hunter - scavengers to have ever existed - create a strikingly original, efficient and for lack of a better term "nasty" eco-morphological package that punched above their own weights in many categories.

They were above all else... awesome... bro.

And finally... can we please stop calling them raptors? That name is already taken!! You may have noticed through the course of these articles that I have bounced a lot between dromaeosaurid and dromie... I probably in retrospect should have used the term eudromaeosaurid through out as they are what I am principally talking about here not microraptorines or unenlagines.

I vote for calling these guys "dromies"and am fully favor of eschewing the befuddled term "raptor".





Cheers!!

Papers

Scientific Reports 5, article no. 12338, July 2015

Fowler, D. W., Freedman, E. A., Scannella, J. B., & Kambic, R. E. (2011). The predatory ecology of Deinonychus and the origin of flapping in birds. PLoS One, 6(12), e28964.

Gignac, P. M., Makovicky, P. J., Erickson, G. M., & Walsh, R. P. (2010). A description ofDeinonychus antirrhopus bite marks and estimates of bite force using tooth indentation simulations. Journal of Vertebrate Paleontology, 30(4), 1169-1177.

Kim, J.Y., Kim, K.S. and Lockley, M.G. 2008. New didactyl dinosaurs footprints (Dromaeosauripus hamanesnsi ichnogen. et ichnosp. nov.) from the Early Cretaceous Haman Formation, south coast of Korea. Palaeogeography, Paleoclimatology, Palaeoecology 262: 72-78


Li, Rihui., Lockley, M.G., Makovicky, P.J., Matsukawa, M., Norell, M.A., Harris. J.D., Liu, M., (2007) Behavioral and faunal implications of Early Cretaceous deinonychosaurian trackways from China. Naturwissenschaften (2008) 95: 185-191 online 

Xing, L., Li, D., Harris, J.D., Bell, P.R., Azuma, Y., Fujita, M., Lee, Y.−N., and Currie, P.J. 2013. A new deinonycho−
723–730.http://www.xinglida.net/pdf/XING_et_al_2012_Deinonychosaurians_Tracks.pdf



"A Long habit of not thinking a thing wrong, gives it a superficial appearance of being right, and raises at first a formidable outcry in defense of custom". Thomas Paine

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Wednesday, July 6, 2016

Making Dromaeosaurids Nasty Again Part III: Life Appearance - Dapper or Deranged?



Skeksis (singular and plural) Antagonists from Jim Henson's 1982 film The Dark Crystal. Concept artist Brian Froud conceived as "part reptile, part predatory bird, part dragon".

Appearance (from wikipedia):

The Skeksis are tall bipeds combining avian and reptilian characteristics. They wear elaborate but threadbare robes of lace, velvet, and brocade which apparently keep the skeksis' constantly decomposing bodies intact and make them look larger and more intimidating. Their heads are beaked like a vulture's but simultaneously sporting curved fangs. They have enlarged bellies and long reptilian tails, as well as curved quills on their backs. They have two pairs of arms but only one functional the other reduced... despite their frail appearance they are powerful creatures.

It should be no great revelation that this post will serve as the most subjective and probably therefore most controversial in this series. Experience in electing novel soft tissue structures in T. rex and Smilodon has  taught me that much...

It should also come as no surprise to readers that I am no great fan of dapper dromaeosaurids - a look that has come into vogue in recent years.



Dapper /'dapper/ adjective (typically of a man) neat and trim of dress, appearance, or bearing.

Deinonycus antirrhopus credit John Conway CC3.0

How did this look evolve? It is not too hard to trace a lineage of inspiration from Gregory S. Paul who retooled dromaeosaurids as feathered and decidedly bird like to John Conway who took a lot from Paul's look and made these animals even more birdy to Emily Willoughby one of the leading contemporary dromaeosaurid paleoartists whom has greatly inspired the dominant ground hawk look.

Acheroraptor credit Emily WilloughbyCC3.0
A commonality in all three of these artist's look is the clean cut juncture on the facial region separating feathered from non-feathered parts. This clean cut visage, almost always combined with an attractive feathery countenance lifted from a modern bird of prey (red tailed hawks and peregrine falcons are common suspects). A look that has been consistently aped and imbued itself into the dominate appearance of these animals in paleoart.

Peregrine Falcon credit Magnus Manske CC2.0

Gregory S. Paul hypothesized a "proto-beak" around the mouth of his dromaeosaurids and other maniraptorans. Basically an area free of integument and slightly cornified. See here and here. Essentially it was an inference made on the perceived - and correct - relatedness to modern birds.

The problem is that we do not have any evidence of a proto-beak in dromaeosaurids or any predatory maniraptorans at all for that matter. Nothing, nada, nunca. Nor do we have any evidence of the type of clean cut juncture depicted by Conway & Willoughby which has influenced current depictions.

Mathew Martyniuk discussed this seldom mentioned meme in an excellent post The First Feathered Dinosaurs (In Art):

"Paul essentially invented the latter meme (half feathered faces) in an attempt to make his theropods look more bird like (by suggesting a sort of beak), and while this was his own speculation, many later artists ran with it, including in early drawings of Sinosauropteryx."

While Conway's and Willoughby's renderings do not necessarily imply the sort of "proto-beak" structure that Paul hypothesized both of these artists kept the clean cut dapper "featherline" which Paul used demarcating a solid break from the feathered region of the head and the bitey jaw region. This trope has imbued itself into countless depictions of dromaeosaurids since, to the point that it is in many ways the de-facto way to depict the heads of these animals in many people's minds. Just remember - if you chose to depict dromaesaurs this way you are merely inheriting a trope that has no basis in evidence of either a proto-beak or a defined juncture between feathers and non-feathery covering on the heads of these animals. Not saying it is impossible that some dromies did not have such a juncture just that it is based on a hypothesis of a proto-beak which has not been borne out evidence wise but remains with us as an attractive speculation.

Indeed feathers covering the entirety of the head (except maybe the nostrils left open ala mammal noses) is what might be the more parsimonious interpretation as suggested by Sinornithosaurus and Zhenyuanlong. With no evidence of a proto-beak in these animals there is no reason to assume feathers did not go all the way to the oral region.


Sinornithosaurus 'Dave' credit DinoGuy2 CC1.0
This actually opens the doors for a lot more play as goes the facial appearance of these animals. As it should be, because we should not expect a lineage of animals that evolved and lived in diverse conditions for over 100 million years to all look a like. Everywhere from fully feathered to yes, naked skin, or in between.

"Go Away" by Lucas-Attwell w/permission Tsaagan mangas. deviantart
You know I loves me some vulturine inspired dromies. I really like how the tail display, arm-wings, contrasting white/dark colors, and jaw are all used together in threat display. As I argued in my last post there is at least as much - if not more - to glean from vultures as analogues to many dromaeosaurids as there is from raptorial accipterids. Also note that the feathers are plumaceous like in an ostrich not the stiff venaceous feathers we have often seen in paleoart.

Tsaagan. credit Matt Martyniuk CC2.5



I am a little surprised at the blowback I receive in electing naked headed, gnarly faced, caruncle ridden dromaeosaurs as a likely look for many of these animals. But why not? I am fully willing to concede my bias for ugly, uncouth, goblin looking critters duh.... I wear my inspirations on my sleeves baked in bong hit residue, blotter acid, splatter films, and swedish death metal. That does not mean I am in fact wholly wrong. More to the point, I would suggest others are less open than I am in conceding their own biases. Do I suspect that some people really have a penchant for the attractive, elegant, and refined look of dromaeosaurids that has come into vogue? Essentially a grounded peregrine falcon or red-tailed hawk? That such elegant, attractive, and appealing visages have a conscious or subconscious appeal to many of the artists and fans who endorse such a look even going so far as to assert "this is how they looked, period". Wrapped up in a nice little bow because of the RPR hypothesis - which as I have mentioned again and again Fowler stated specifically dromaeosaurids were not as strong graspers as modern accipterids - fueling the typological thinking to dress up a Deinonychus as a grounded red-tailed hawk? And that people who have such a definite and emotional attachment to such a look would be dismissive and threatened by my interpretation asserting a more vulturine influence? Nah, that never could happen snark, snark...

Just to keep in mind I am getting my inspiration from birds too, and not all birds are concerned with looking regal and elegant...

For every grey-crowned crane I can raise you a helmeted hornbill;

helmeted hornbill. Rhinoplax vigil Doug Janson CC3.0
For every great blue heron I give you a marabou stork;

Marabou Stork (Leptoptilos crumeniferus) credit Rusty Clark CC2.0
(end of rant)....



Truth is we do not have a lot to go on in terms of facial appearance of the medium to larger dromaeosaurids that lived in open and/or hot & arid environments. Painting with broad strokes I would lean more towards fully feathered heads for smaller dromies/small game specialists especially in closed temperate environments - essentially Liaoning. But for dromies that were out in the open, fighting and competing over carcasses, going toe to toe with carchs, abelisaurids, and tyrant lizards, in hot and/or arid environs a naked head with fleshy adornments is a defensible position. Many of the more famous dromies such as Velociraptor, Deinonychus, Utahraptor, and Dakotaraptor fall in this category.

credit Charlie Hamilton Jones Getting Cozy With Vultures
Large exposed patches of skin on the head and neck can serve a thermoregulatory function and also social signaling. Blood can be flushed into caruncles, necks flaps, and other skin adornments in colorful threat dominance displays as occurs in condors.

Andean Condor credit Kevin Law CC2.0
Whenever I talk about fleshy skin adornments on theropods - including large lips - there is a consistent critique that people chime in with: "but these areas would be targets for biting by conspecifics and get snipped right off!?!"

Let me offer some rebuttals (takes a deep breath):

1) Losing a chunk or flap of skin is still preferable to losing an eye or getting a bite on the neck or vertebral column which could have fatal results. That being said skin can be amazingly strong, elastic, and (best  of all) it grows back. Hyenas, bears, badgers and yes vultures are often noted for the strong and elastic properties of their skin that allow them to suffer abuse that would seriously lacerate lesser skinned animals. Theropods - and especially combative dromies - had all the reason to not only have such thick and elastic skin but abundant skin derived display structures. Just look at the skull of a male andean condor, there is no tell tale osteological signifier that it looked like the mug above.

2) Which brings me to my next point. We already have compelling and irrefutable osteological evidence of display structures on other theropod skulls (Dilophosaurus, Guanlong, Monolophosaurus etc. etc.). That these animals would grow such features in a highly visible and vulnerable part of the body complete with thin struts of bone - and they were not snipped right off - is all the more compelling reason to suspect a more widespread and outlandish panoply of soft tissue structures throughout theropoda (and many dinosaurs in general) that would not preserve. Especially among those theropods that were regularly coming together socially at large carcasses in feeding events/social gatherings. Dromies certainly count in that regard. In fact we should predict such structures.

3) Which leads right into my next point - prediction met (sort of) !! By now many readers have doubtless heard of the (as yet undescribed) evidence of a large distensible gular neck structure on a Tarbosaurus bataar. If this story pans out we do have evidence of a fleshy display structure on a lineage of the most bitey theropods of all time in the most vulnerable part of the body. So putting a highly visible, likely brightly colored display structure on the neck of the most powerfully biting terrestrial tetrapods of all time still panned out in the Darwinian struggle.

4) Such critics have probably never really been in a fight or done poorly in one... really don't take it as an insult because fighting and violence in humans is not really a good trait to endorse. But looking at what professional fighters and strikers do and the tactics that they use can be useful. One common tactic  used in boxing is to intentionally offer up a shot that puts your opponent in a vulnerable position by feinting a move and then counter-striking.  Let's go through what happens when a "vulnerable" fleshy skin adornment (or large lips) are bitten by another theropod.

I In a dispute one theropod bites the skin flap on the chin of another theropod. Due to the strength and elasticity of this skin it is not simply cleaved right off but instead substantial yanking and pulling would be needed to remove such structures.

II As the theropod that did the biting - let's call it theropod A - pulls and yanks that piece of skin off the bitten theropod - theropod B - and finally cuts clean the skin structure the momentum of the pull off will move theropod A downward and lateral from theropod B.

III At this point it is theropod B - the bitten theropod - that has tactical advantage. Theropod A in the course of yanking off a chunk of skin has put its head and neck inferior to theropod B.

IV Theropod B can now attack theropod A and get a potentially fatal or devastating bite to the back of the neck or head of theropod A. More importantly theropod A can not retaliate when bitten from this position at the back of the neck/skull.

V Theropod B has lost a piece of skin that can potentially grow back. Theropod A has in its miscalculations put itself in a vulnerable position and although it successfully inflicted non-fatal damage by removing a chunk of skin it may potentially lose its life because in doing so it left the back of its head and neck open.

"Bite my lips I dare ya'" credit Tiia Monto CC4.0
Watch brown bears fight. Their big, jangly, fleshy lips are mere inches from one another yet they are not targeted. Because bears are better tactical fighters than most people. Bears know better than to commit to a non-fatal attack that might leave them open in the end.

One final word on theropod facial biting/skirmishes. I suspect the vast majority of bites were not the bone scraping/puncturing potentially fatal traces we see in the fossil record. The overwhelming majority of interactions that went beyond theatrical displays and gesticulations were probably the fast little nips and non-committal bites we see among canids and social feeding birds. Many of these bites would not even break the skin.

Ruppels Vulture bites another, showcases tough, elastic skin. credit. credit Charlie Hamilton Jones. natgeo
I will delve more into display structures in theropods in the future because I think that they are a fascinating topic for exploration. Instead of asking how much or how little these feature were found in theropods - as you can tell I suspect that they were quite widespread - I think we should be asking why are mammalian predators (and I guess you can extend this question to predatory monitor lizards) so impoverished when it comes to display features?

A Long History Of Dromaeosaurid Evolution Lots of Room For Variation

If we accept a middle Jurassic origin for dromies of about 167 mya that gives us more than 100 million years of dromaeosaurid tenure of small and medium sized carnivorous theropod. That is longer than felids or canids have been around. More importantly that is longer than ratites have been around.

I really want to drive home the ratite comparison because dromaeosaurids are increasingly likely secondarily flightless - probably evolving from something like Microraptor that could glide if not fly in a limited capacity. So if we look at ratites it becomes apparent that they have done all sorts of weird things with their feathers once they became permanently grounded. Especially so with their flight feathers. Ostriches no longer have the stiffened vennaceous wing feathers of flighted birds but more open plumaceous ones. Cassowaries have quilled wings. These options are real possibilities for dromaeosaurids but should be analyzed and imbued within a likely evolutionary/ecological framework.

Cassowary. credit Gambier Bolton
In my last post I depicted a Dakotaraptor that veered very far away from other restorations. What I put in that rendering is quilled tail feathers. No need to incur drag when you are that cursorially adaptated. No longer a flighted animal or even one that could glide at that size I posited quills on the tail as a weaponized exaptation useful for whipping around at theropod dinner parties and also for rattling in threat display.  Visual, auditory, and physical threat and intimidation displays should all be on the table when considering dromies. They were likely some of the most gruesomely theatrical animals when gathered in group feeding bouts in the history of terrestrial carnivores.


I also gave Dakotaraptor a striking white feather patch on the front of its chest for bold display and intimidation. Such bold white patches - when contrasted against darker integument - are common in birds of prey and also some mammals such as various species of Asiatic bear.

Ursus thibetanus. credit Guerin Nicolas. CC3.0
I took this notion of feather disuse and even extreme reduction further in a rendering showcasing a Dromaeosaurus feeding scrum on a non-descript chasmosaurine ceratopsid. An azhdarchid and a troodon are looking on waiting for scraps.

feeding scrum by Duane Nash click on image for bigger shot
As you can see I really took the hyena analogy to the extreme even to the spotted scruffy coat. I reduced the wing feathering and eschewed tail feathers completely as this ground based, running, scavenging dromie had little need for them.



I also gave Dromaeosaurus a thick neck mane of coarse feathers for protection during skirmishes.


100 million years of terrestrial evolution from likely flighted ancestors allowed for substantial variation in appearance and function of dromaeosaurids; modern flightless birds show that flight feathers can become plumaceous or quilled; aggressively combative, usurping, and scavenging dromaeosaurids especially in hot and/or arid environs likely featured large areas of the head, neck, and chest bare or with feather reductions; such areas could have sported extreme skin adaptations that offered thermoregulatory, protective, social, and intimidatory benefits; for these dromaeosaurids new world vultures (cathartidae) and old world vultures (accipteridae) might offer more useful analogue behaviorally and physically than raptorial birds of prey (accipteridae); feathers could additionally have been arranged in coarse manes or thick tufts around the neck for protection as well as bold white/dark contrasting areas for intimidation.

One final note and this has to do with anthropomorphism - the ascription of human values, conceits, and emotions onto animals. One charge I have seen leveled at me is that I, to paraphrase, "depict many of my animals intentionally weird, ugly, or unattractive". To which I reply "duh, goal achieved".

I have always been transparent with my inspirations culturally on this blog - informed as I am by ugly music and ugly movies. I think it important that researchers be transparent with their inspirations, not just their scientific ones, to most reveal potential biases. We are all primarily cultural critters and it would be naive to think even the strictest and staunchest scientists are not first and foremost cultural creatures.

So when one looks at vultures gobbling and skirmishing over a carcass or the scruffy, uncouth appearance of hyenas and their cackles and the words "horrific", "disturbing", "ugly", and "revolting" are bandied about is this a cultural reaction or a more intrinsic, base natural one? Let us flip our way of thinking about combative scavengers... do we think about them with these conceits in our mind because of culture, or, because we ourselves are animals and most animals want to move away from the sight of such animals feeding? That is the that the shock, the visual awe, the intimidation we feel at the sight of these feeding events is the same gut level emotional response other animals feel: "I don't want to get near this cancerous looking, tumor faced, loud, shrill, dominating, repellent, and combative animal not because of some cultural tradition but because I too am an animal and I react on a visceral level to this display?"




Coming up a new hypothesis on dromaoesaurid biting technique because it really is all about the teeth...


"A Long habit of not thinking a thing wrong, gives it a superficial appearance of being right, and raises at first a formidable outcry in defense of custom". Thomas Paine

Support me on Patreon.
Like antediluvian salad on facebook. Visit my other blog southlandbeaver.blogspot
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